Conventionally, an expander-integrated compressor has been known in which a compression mechanism and an expansion mechanism are disposed vertically within a closed casing (see, for example, WO 2005/088078and JP 2003-139059 A).
The expander-integrated compressor disclosed in FIG. 2 of WO 2005/088078 includes a casing formed of a closed casing as well as an expansion mechanism, a motor, and a compression mechanism that are disposed inside the casing. The expansion mechanism, motor, and compression mechanism are disposed sequentially from the upper part toward the lower part. A rotating shaft of the compression mechanism extends upwards, and the expansion mechanism is coupled to this rotating shaft. That is, the rotating shaft of the compression mechanism also is used as the rotating shaft of the expansion mechanism. An oil reservoir is provided in the bottom portion of the casing. An oil pump is provided at the lower end of the rotating shaft, and an oil supply passage is formed inside the rotating shaft. In the expander-integrated compressor, the oil pumped up by the oil pump passes through the oil supply passage to be supplied to each sliding part of the compression mechanism and expansion mechanism.
In the above-mentioned expander-integrated compressor, the rotating shaft penetrates through the compression mechanism to pump the oil up from the oil pump provided at the lower end of the rotating shaft. Accordingly, a rotary compression mechanism often is used as the compression mechanism.
The rotary compression mechanism includes a cylinder, a piston that eccentrically rotates inside the cylinder, and a partition member that partitions the space inside the cylinder into a low-pressure side compression chamber and a high-pressure side compression chamber together with the piston. The partition member slides with respect to the cylinder as the piston rotates eccentrically. In the rotary compression mechanism, since the partition member plays an important role in partition the compression chamber inside the cylinder, it is necessary to supply a sufficient amount of the oil to the partition member to lubricate and seal it.
However, the partition member is provided on the outer circumferential side of the rotary compression mechanism and therefore is located away from the oil supply passage formed inside the rotating shaft. Accordingly, the partition member is not lubricated sufficiently and thereby, for example, seizing may occur due to friction. Furthermore, since insufficient oil supply results in a decrease in sealing force, there also is a possibility that compression performance decreases dramatically.
Therefore, in the expander-integrated compressor described above, in order to solve the shortage in oil supply to the partition member, the rotary compression mechanism is immersed in the oil contained in the oil reservoir and thereby the oil is supplied directly from the oil reservoir to the partition member.
However, the oil contained in the oil reservoir is supplied to the respective sliding parts of both the compression mechanism and the expansion mechanism through the oil supply passage. Furthermore, part of the oil supplied to the respective sliding parts is discharged to the outside of the casing together with a flow of working fluid. Therefore, in the expander-integrated compressor, the oil contained in the oil reservoir tends to be reduced as compared to the case where only a compression mechanism is included. Particularly, for example, at the time of startup of a refrigeration cycle apparatus or at the time of a change in the pressure-temperature conditions, the oil contained in the oil reservoir tends to be reduced. However, in the expander-integrated compressor, since the oil pump is provided at the lower end of the rotating shaft, a predetermined amount of the oil continues to be supplied to the expansion mechanism even after the oil contained in the oil reservoir is reduced. Accordingly, the oil contained in the oil reservoir further is reduced.
When the oil contained in the oil reservoir is reduced and the oil level is lowered, the oil cannot be supplied to the partition member from the oil reservoir. Accordingly, the sealing performance of the compression mechanism deteriorates. This results in unstable operation of the compression mechanism, and thereby the compression efficiency decreases dramatically. Furthermore, the partition member and the cylinder are worn away due to the lack of lubrication. This also decreases the compression efficiency of the compression mechanism.
The compression mechanism serves as a power source for circulating a working fluid of the refrigeration cycle apparatus. Therefore, the effect of the operating condition of the compression mechanism on the refrigeration cycle apparatus is much greater than that of the expansion mechanism on the refrigeration cycle apparatus. Accordingly, when the operation of the compression mechanism becomes unstable, the refrigeration cycle apparatus also becomes unstable, which results in a problem in that the refrigeration capacity decreases.